This invention relates to an embroidery or stitch pattern sewing machine for forming initials, symbols, and other stitch patterns by embroidering, by means of relatively moving a workholder holding a shirt, handkerchief, and other workpieces to a needle capable of vertically reciprocating and also laterally oscillating in a plane based on prestored pattern data corresponding to initials, symbols, and other stitch patterns in memory means, made with many stitches formed on the workpiece.
In the conventional automatic stitch pattern sewing machine of this kind, each position data of pattern information indicating plural stitch forming positions corresponding to a desired stitch pattern or embroidery was consecutively stored on a memory means such as a paper tape, etc., and a needle and an embroidery frame holding a workpiece were relatively moved based on those position data for forming the embroidery or stitch pattern on the workpiece with many stitches formed by means of the vertical movement of the needle. In this mode of formation of the stitch patterns, fineness of an stitch pattern made on a workpiece depends entirely upon the pattern information stored in the memory means, so the preparation of the pattern information is regarded as of extreme importance. Variety of pattern information preparing methods are already proposed. Particularly in case of forming stitch patterns, on the workpiece, of letters such as Chinese characters, Japanese Katakana characters, English characters or Arabic numerals, the following two ways are most popular, one being a way of forming a pattern of a letter with stitches formed substantially perpendicular to each component line portion thereof and the other being a way in which only horizontally extending line portions are given perpendicular stitches and the rest portions are given horizontal stitches. The pattern formed in those ways can not be said fine because of irregulalities of the stitch direction according to component elements of a letter. In another proposition all of the component line portions are formed with exclusively vertical stitches or horizontal stitches. In this way, some line portions are stitched intermittently or disconnectedly in several sections, and some other line portions are seamed with long horizontal or vertical stitches. Those stitch patterns still leave a problem of not being fine in its appearance due to the above irregulalities.
The inventor of this invention executed a series of statistical analyses in respect of the direction of various component elements of the letters, such as Chinese characters, Japanese Katakana characters, English characters, Arabic numerals, etc. for finding a result in which line portions horizontally or vertically extending are of large percentage while line portions extending at an angle of approx. 30.degree. against a horizontal reference line being of small percentage. After a long studying about the statistical data and the earlier mentioned ways of stitch formation, he discovered that stitches with only one direction which form an angle of about 30.degree. against a horizontal reference line will make a fine embroidery pattern of those letters.
As a device of prior art for forming a stitch pattern on a workpiece exclusively with slant stitches at a predetermined angle against a horizontal reference line in a letter of the like, U.S. Pat. No. 2,597,686 can be cited.
In this prior art technology following problems, for example, are still unsolved, one being requirement to high level skilfulness of the operator because of manual adjusting of the shift amount of the workholder and the oscillation amount of the needle, and another being inevitable irregulalities seen in the stitch pattern on the workpiece.